The present invention relates to a 2D barcode scanner comprising a housing having a reading window and a digital camera arranged in the housing for detecting the area of the reading window either directly or via one or more deflecting mirrors.
2D barcode scanners capture a one-dimensional or linear barcode, a QR code or other two-dimensional codes, all of which are hereinafter designated as “barcodes,” by using a digital camera and electronic evaluation logic, coupled to the digital camera, which processes the image captured with the camera and determines the barcode number digitally. Using a 2D barcode scanner of this type, information arranged in a two-dimensional area can be read and evaluated advantageously in one step.
According to the prior art, 2D barcode scanners comprise a housing with a reading window for viewing the barcode that is placed in front of it. Arranged at the side of the reading window that faces away from the barcode to be read is a digital camera, which captures images that cover the reading window directly or via a deflecting mirror arrangement. Providing deflecting mirrors achieves a compact design since the distance between the camera lens and the reading window required for capturing the entire reading window is realized via the deflecting mirror.
As a rule, cameras integrated in 2D barcode scanners have integrated illumination in the form of one or more internal LEDs in order to illuminate the barcode area and thus to ensure an error-free image capture. However, the illumination achievable thereby is in practical applications not sufficient to capture the entire area of the reading window or to capture special barcode designs. This is the case, for example, when using barcode colors that have special properties in a defined range outside the visible light spectrum. These can be captured only by sufficient illumination in this defined range outside the visible light spectrum. In addition, the arrangement of the integrated illumination near the camera lens easily causes reflections at the reading window, which makes the evaluation of the data difficult or impossible.
For these reasons, it is known in the art to provide external light sources, e.g., LEDs, which can illuminate with sufficient brightness and homogeneity a barcode that is to be read and that is arranged on the side of the reading window facing away from the digital camera.
Light reflections arise here as well on the inside of the reading window even with anti-reflective glass. As a result the digital camera disadvantageously also captures a mirror image of the illumination that is superimposed on the barcode to be read. As rule, very bright spots, so-called hotspots, appear in the image of the digital camera, which can result in over-controlling the camera, making error-free barcode evaluation no longer possible.
Distributing the illumination to multiple light sources would decrease the intensity of the brightness of the individual hotspots but would disadvantageously increase the number of hotspots. Furthermore, improving and optimizing the anti-reflective coating on the inner side of the 2D barcode scanner's reading window would work only for a narrow wavelength range and would disadvantageously require illumination in a narrow bandwidth; that is, illumination in a very narrow frequency band, which would prevent reading of barcodes across the full color spectrum or even of spectra outside the visible wavelength range.
Another possibility of avoiding hotspots involves illuminating the reading window at an angle to the optical axis of the digital camera from the side, which leads to homogeneous illumination in the plane of the reading window. This also reduces the interfering hotspots or shifts them outside the image area, respectively. However, the disadvantage of this method is that the illumination and reading of the barcode are optimal only in one plane. Due to the very poor achievable homogeneity of the illumination across the depth, the result is unsuitable for illuminating areas further away from the reading window.